DFS Visitor Concept

This concept defines the visitor interface for depth_first_search().
Users can define a class with the DFS Visitor interface and pass an
object of the class to depth_first_search(), thereby
augmenting the actions taken during the graph search.

Associated Types

Valid Expressions

This is invoked on every vertex of the graph before the start of the
graph search.

Start Vertex

vis.start_vertex(s, g)

void

This is invoked on the source vertex once before the start of the
search.

Discover Vertex

vis.discover_vertex(u, g)

void

This is invoked when a vertex is encountered for the first time.

Examine Edge

vis.examine_edge(e, g)

void

This is invoked on every out-edge of each vertex after it is discovered.

Tree Edge

vis.tree_edge(e, g)

void

This is invoked on each edge as it becomes a member of the edges that
form the search tree.

Back Edge

vis.back_edge(e, g)

void

This is invoked on the back edges in the graph. For an undirected
graph there is some ambiguity between tree edges and back edges since
the edge (u,v) and (v,u) are the same edge, but both the
tree_edge() and back_edge() functions will be
invoked. One way to resolve this ambiguity is to record the tree
edges, and then disregard the back-edges that are already marked as
tree edges. An easy way to record tree edges is to record
predecessors at the tree_edge event point.

Forward or Cross Edge

vis.forward_or_cross_edge(e, g)

void

This is invoked on forward or cross edges in the graph. In an
undirected graph this method is never called.

Finish Edge

vis.finish_edge(e, g)

void

This is invoked on each non-tree edge as well as on each tree edge after
finish_vertex has been called on its target vertex.

Finish Vertex

vis.finish_vertex(u, g)

void

This is invoked on vertex u after finish_vertex has
been called for all the vertices in the DFS-tree rooted at vertex
u. If vertex u is a leaf in the DFS-tree, then
the finish_vertex function is called on u after
all the out-edges of u have been examined.

Models

Python

To implement a model of the DFSVisitor concept in Python,
create a new class that derives from the DFSVisitor type of
the graph, which will be
named GraphType.DFSVisitor. The events and syntax are
the same as with visitors in C++. Here is an example for the
Python bgl.Graph graph type: